1. Field of Invention
This invention relates to helicopters which have their main rotor blades foldable over the tail cone and their tail rotor pylon foldable about a tail cone vertical hinge from a fore-and-aft flight position through an angle of approximately 180.degree. into a position in which it lies alongside the tail cone so that the helicoter can be stored in a shipboard hangar or transported in the elevator of an aircraft carrier for storage beneath the deck.
More particularly this invention is concerned with the pilot operated pitch control cable for the tail rotor blades and a system of pulleys and links for maintaining a continuous cable with a substantially constant tension on this cable throughout the full fold cycle of operation of the tail rotor pylon.
2. Description of the Prior Art
U.S. Pat. No. 3,901,464, issued Aug. 26, 1975 to Bennett R. Arnstein et al shows in FIGS. 2 and 3 a system of pulleys and linkage for maintaining constant tension of a cable extending from the fuselage of an airplane to a spoiler on a variable sweep wing. Arnstein provides two links of equal length pivotally connected together at their free ends and having their other ends pivotally connected to fuselage 210 and wing 220 respectively by pivots spaced from hinge line 250 a distance equal to the length of the links, thus forming a parallelogram linkage. This linkage, however, requires that the floating pulley 34 mounted on the pivot common to both links be twice the diameter of pulleys 33,37 at the ends of the links which are pivoted on the fuselage and wing respectively. This structure is adequate for a swept wing where the angle of sweep is only about 45.degree. and there is plenty of room for the linkage to operate. It is wholly inadequate for use with a helicopter tail rotor pylon which has a fold angle of approximately 180.degree. and is located in the end of a tail cone which is 14" in diameter, as will be pointed out hereinafter.